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Update on Less invasive prenatal testing

Non-invasive tests have become cheaper and are more available to women in rural areas.

The basic Harmony test (trisomy 13, 18 & 21) now costs $425. A Medicare rebate is not available for this test.

Another local lab offers a basic Generation test costing $395 and an extended test for $695

I have refined what I offer in the last last few year,

Will offer a dating scan to confirm dates

NIPT after 10 weeks if you can afford it

First trimester ultrasound and screening bloods if you have had a NIPT, or risk assessment if no NIPT. This is done between 11 to 13+6 weeks.

31 March 2018

The most recent ANZJOG has two papers and an editorial about non-invasive prenatal testing for certain fetal genetic disorders.

This should really be called less invasive as unlike some DNA testing it does require a blood specimen. But it is certainly less invasive than an amniocentesis or chorionic villus sampling (CVS) with the attendant risk of miscarriage.

Although operator dependent, the risk of miscarriage with CVS is between 1:100 to 1:200; whilst there is less risk from an amniocentesis; 1:200 to 1:300. CVS can however be performed earlier in the pregnancy.

The risk of miscarriage and stillbirth may be increased by factors such maternal age and weight, previous miscarriage, or stillbirth, low PAPP-A, high high fetal nuchal translucency, pre-existing diabetes, ovulation induction. chronic hypertension and smokers.

Obviously it would not be acceptable to do these tests on all pregnancies. Not every woman want to know her child’s genetics. To many the option ending a pregnancywith Down Syndrome is unacceptable.

In South Australia, screening done by SAMSAS at the Women’s & Children’s Hospital.

Screening requires

blood at 9 to 13 weeks

nuchal translucency at 11 to 13+6 weeks

For practical purposes I usually organise testing at 11 to 12 weeks with the ultrasound first to confirm dates then the blood drawn if dates are accurate.

The detection rates for Down Syndrome with this test are

Serum biochemistry alone 70.1%

Ultrasound alone 72.7%

Serum biochemistry + Ultrasound 88.3%

I offer screening to all pregnant women as a way to better define the risk of having a baby with Down Syndrome than age alone. For an estimate of age related risk I use SAMSAS update 15.

I use the risk of greater than 1:250 to recommend an invasive test. If the test then identifies an abnormality, the woman may be offered a termination of the pregnancy. I usually offer my personal view that if I would never terminate a pregnancy then I wouldn’t undertake the screening test.

Some women still want to know more about their risk but baulk at the risk of the CVS or amniocentesis. For them the non-invasive test is attractive.

For women who fall into the more than high risk screening group the non-invasive test is also attractive.

There is no Medicare funding; nor is it covered by private insurance companies. The test cost will $900 to $1250.

The blood test has to be done in a major capital city on a specific day. So there is the cost of the journey to consider. The blood is then flown to the US for testing. Interestingly, Tasmanian women can have it done at the Royal Hobart but pay a $100 premium over those in Melbourne.

There is a wait for 7 to 10 days.

Accuracy is dependent upon fetal DNA yield.

The tests may be performed from 9 weeks which is prior to the nuchal translucency ultrasound and would necessitate a dating scan if dates are uncertain.

The American College of Obstetricians and Gynecologists Committee on Genetics issued a position statement on non-invasive prenatal testing for fetal aneuploidy in December 2012:

“Noninvasive prenatal testing that uses cell free fetal DNA from the plasma of pregnant women offers tremendous potential as a screening tool for fetal aneuploidy. Cell free fetal DNA testing should be an informed patient choice after pretest counseling and should not be part of routine prenatal laboratory assessment. Cell free fetal DNA testing should not be offered to low-risk women or women with multiple gestations because it has not been sufficiently evaluated in these groups. A negative cell free fetal DNA test result does not ensure an unaffected pregnancy. A patient with a positive test result should be referred for genetic counseling and should be offered invasive prenatal diagnosis for confirmation of test results.”

I believe that RANZCOG and RCOG are still considering how this test fits into their guidelines for prenatal testing.

For the time being, given I do not do CVS or amniocentesis my plan is to continue to offer all my pregnant patient the SAMSAS screen and if they can afford the test to discuss it with the obstetrician in the tertiary centre prior to undergoing an invasive test. I know some women would struggle with the cost but the test may well avoid having a CVS or amniocentesis with its attendant risks.

4 thoughts on “Update on Less invasive prenatal testing”

Your conclusion is also my practice as well. I used to also think about discussing with the women not going through with the screening if they would not consider termination anyway. I have recently changed my practice on this and now talk about still offering the testing anyway because if the child is very high risk for Down’s it may allow the family to educate themselves and mentally prepare themselves for the possible eventuality that their child may have a genetic syndrome and prepare for the comorbidities and challenges that are related to this.

Do you spend 6 to 7 months thinking about having a potentially disabled child on the basis of a screening test alone and then be relieved that child appears normal when it is born?

Pregnancy can be a stressful time for parents without that hanging over their head. Is is better to blissfully unaware?

Something that I also tell parents is that knowing their child’s chromosome doesn’t tell them about who their child will be. I’m certain that a lot of evil bastards in history had 46 healthy chromosomes

This is where a good GP has the advantage, if you don’t already, you can make the time to get to know your patient.